Coating compositions

ABSTRACT

COATING COMPOSITIONS CONTAINING, AS THE BINDER (A) 45-15% BY WEIGHT OF AN AMINOPLAST OR A LOWMOLECULAR PRECURSOR THEREOF; AND (B) 55:85% BY WEIGHT OF AT LEAST DIFUNCTIONAL ESTERS CONTAINING PREDOMINANTLY HYDROXYL GROUPS AND OPTIONALLY CARBOXYL GROUPS AS THE FUNCTIONAL GROUPS AND HAVING AN AVERAGE MOLECULAR WEIGHT OF LESS THAN 600 AND PRODUCED BY THE ESTERIFICATION OF I. AN ALCOHOL REACTANT CONSISTING ESSENTIALLY OF: (1) 0-50 MOLAR PERCENT OF ONE OR MORE ALIPHATIC POLYOLS OF 3 OR 4 HYDROXYL GROUPS AND 3-6 CARBON ATOMS, AND (2) 100-50 MOLAR PERCENT OF A DIOL COMPONENT CONSISTING ESSENTIALLY OF: (A) AT LEAST 70 MOLAR PERCENT OF ONE OR BOTH OF ETHYLENE GLYCOL AND 1,2-PROPANEDIOL, AND (B) UP TO 30 MOLAR PERCENT OF ONE OR MORE OTHER ALIPHATIC OR CYCLOALIPHATIC DIOLS WHOSE HYDROXYL GROUPS ARE SEPARATED BY 2-8 CARBON ATOMS, AND 0 TO 2 OF THE CARBON ATOMS IN THE CHAIN ARE SUBSTITUTED BY OXYGEN ATOMS WHICH ARE SEPARATED FROM EACH OTHER AND FROM THE HYDROXYL GROUPS BY AT LEAST 2 CARBON ATOMS, AND II. AN ACID MIXTURE CONSISTING ESSENTIALLY OF: (1) 80-200 MOLAR PERCENT OF ONE OR MORE AROMATIC OR CYCLOALIPHATIC DICARBOXYLIC ACIDS WHOSE CARBOXYL GROUPS ARE POSITIONED ORTHO OR META OR A FUNCTIONAL ACID DERIVATIVE THEREOF CONVERTIBLE TO AN ESTER OF THE ALCOHOL REACTANT, AND (2) 20-80 MOLAR PERCENT OF AT LEAST ONE ASTURATED ALIPHATIC DICARBOXYLIC ACID OF 4-12 CARBON ATOMS OR A FUNCTIONAL ACID DERIVATIVE THEREOF CONVERTIBLE TO AN ESTER OF THE ALCOHOL REACTANT ARE CURED AT LOW TEMPERATURES WITHOUT LOSS OF BAKING STABILITY EMPLOYING AS CURING CATALYST 0.7-2% BY WEIGHT OF ONE OR BOTH OF MALEIC ACID AND OXALIC ACID.

United States Patent Ofice US. Cl. 260-850 8 Claims ABSTRACT OF THE DISCLOSURE Coating compositions containing, as the binder (A) 45-15% by weight of an aminoplast or a lowmolecular precursor thereof; and

(B) 55-85% by weight of at least difunctional esters containing predominantly hydroxyl groups and optionally carboxyl groups as the functional groups and having an average molecular weight of less than 600 and produced by the esterification of I. an alcohol reactant consisting essentially of:

( 1) -50 molar percent of one or more aliphatic polyols of 3 or 4 hydroxyl groups and 3-6 carbon atoms, and

(2) 100-50 molar percent of a diol component consisting essentially of: (a) at least 70 molar percent of one or both of ethylene glycol and 1,2-propanediol, and (b) up to 30 molar percent of one or more other aliphatic or cycloaliphatic diols whose hydroxyl groups are separated by 2-8 carbon atoms, and 0 to 2 of the carbon atoms in the chain are substituted by oxygen atoms which are separated from each other and from the hydroxyl groups by at least 2 carbon atoms, and

II. an acid mixture consisting essentially of:

(1) 80-200 molar percent of one or more aromatic or cycloaliphatic dicarboxylic acids whose carboxyl groups are positioned ortho or meta or a functional acid derivative thereof convertible to an ester of the alcohol reactant, and

(2) 20-80 molar percent of at least one saturated aliphatic dicarboxylic acid of 4-12 carbon atoms or a functional acid derivative thereof convertible to an ester of the alcohol reactant are cured at low temperatures without loss of baking stability employing as curing catalyst 0.7-2% by Weight of one or both of maleic acid and oxalic acid.

BACKGROUND OF THE INVENTION This invention relates to novel low temperature curing coating compositions.

Application Ser. No. 135,691, filed Apr. 20, 1971, relates to coating compositions containing, as the binder (A) 45-15% by weight of an aminoplast or a lowmolecular precursor thereof; and

(B) 55-85% by Weight of at least difunctional esters containing predominantly hydroxyl groups and optionally carboxyl groups as the functional groups and having an average molecular weight of less than 600 and produced by the esterification of I. an alcohol reactant consisting essentially of:

(1) 0-50 molar percent of one or more aliphatic polyols of 3 or 4 hydroxyl groups and 3-6 carbon atoms, and

3,819,757 Patented June 25, 1974 2) 100-50 molar percent of a diol component consisting essentially of: (a) at least 70 molar percent of one or both of ethylene glycol and 1,2-propanediol, and (b) up to 30 molar percent of one or more other aliphatic or cycloaliphatic diols whose hydroxyl groups are separated .by 2-8 carbon atoms, and 0 to 2 of the carbon atoms in the chain are substituted by oxygen atoms which are separated from each other and from the hydroxyl groups by at least 2 carbon atoms, and

H. an acid mixture consisting essentially of:

(1) -20 molar percent of one or more aromatic or cycloaliphatic dicarboxylic acids whose carboxyl groups are positioned ortho or meta or a functional acid derivative thereof convertible to an ester of the alcohol reactant, and

(2) 20-80 molar percent of at least one saturated aliphatic dicarboxylic acid of 4-12 carbon atoms or a functional acid derivative thereof convertible to an ester of the alcohol reactant.

Because of the low viscosity of the binder, coating compositions can be produced which can be applied with low amounts of or in the absence of solvent. After baking, coatings are obtained having superior properties.

For the curing of these varnishes at low temperatures, p-toluenesulfonic acid is customarily added as the crosslinking catalyst. However, this additive has the disadvantage that the baking stability of the varnish coatings is reduced.

In US. Pat. 2,683,100, maleic acid, phthalic anhydride, ammonium biphosphate, styrene dichloride, bromonaphthols, and 2,4-dichloro-1-naphthol are described as the catalysts for the cross-linking of polyesters on the basis of terephthalic acid, an aliphatic dicarboxylic acid, and ethylene glycol with, for example, hexakis[methoxymethyl]melamine. From the disclosure of this patent, it is surprising that, for the present binder system, only one of the enumerated compounds can advantageously be utilized as the catalyst, whereas the other compounds, disclosed as being equivalent in their effect, cannot be employed.

In German Unexamined Published Application DOS 1,644,815, maleic acid and p-toluenesulfonic acid, inter alia, are described as catalysts for reducing the baking temperature of coating compositions formed from polycondensation products having hydroxyl and/or carboxyl groups and of reaction products from a polyamine, polyalcohol or an amino alcohol, and N-alkoxymethyl isocyanates, optionally with the addition of melamine or ureaformaldehyde resins. In this reference, maleic acid and p-toluenesulfonic acid, for example, are employed as equivalents. However, in the binder system of the present invention, these compounds result in diametrically op- --posed characteristics with respect to baking stability.

It is an object of this invention to provide a catalyst for the above-described binder system which does not impair the baking stability.

SUMMARY OF THE INVENTION DETAILED DISCUSSION The catalyst preferably is present in amounts of about 1.0-1.5 by weight. Maleic acid is especially effective.

The coating compositions employed herein can be cured with p-toluenesulfonic acid, usually within 30 minutes at 150 C. When exposing the thus-cured systems to elevated temperatures, or baking them for a longer period of time at higher temperatures, a partial disintegration of the stream through the mixture, in accordance with the following time-temperature plan: 2 hours at 140 C.; 2 hours at 160 C.; 4 hours at 180 C.; 4 hours at 190 C.; and 4 hours at 200 C. During this time, 25 ml. of water in total are driven The clear, colorless ester mixture has an film network occurs, resulting in deficient film properties, 5 acid number of 2.5 mg. KOH/g. and a hydroxyl number of as well as in a more or less marked yellow discoloration. 454 mg. KOH/g., corresponding to an average molecular This defective thermal stability is called minor baking weight f 245, stability. This phenomenon could have disadvantageous effects when the baking procedure is impaired, especially Produchon of varmsh when the belt comes to a standstill when coating accord- The thus.obtained ester mixture i i d i h h mg to the c011 coating P f amount set forth in the table below of the acidic catalyst The attePlpt obtam usmg other Customary CataIYStF and stirred at room temperature until complete dissolution tartanc f monobutyl phosPhalie Phosphonc has occurred. Of the thus-obtained mixture, 70.3-70.6 acld, systems which result, after baking 1n a wide tempcl' parts is mixed with 29.7 parts of a commercially available We g a 1n coatmgs havmg mvarlably saflsfactory film etherified hexamethylolmelamine which is liquid in subpropertles, yielded unsatisfactory results since, even after stance. baking for one-half hour at temperatures of above 200 Production f an Enamel C., soft and insufiiciently cross-linked films were obtained. Use of 1-2% by weight of phthalic acid, phthalic anhy- For preparing an enamel, the clear varn sh, optionally dride, terephthalic acid, malonic acid, succinic acid, after adding a small amount of solve p f Wlth glutaric acid, adipic acid and maleic anhydride yielded titanium dioxide 1n the deslred binder-pigment ratlo (for satisfactory film hardness values only after baking for example 2:1). one-half hour at temperatures of above 220 C. These P 0d {0 d T of the C0 fn s temperatures usually are not employed over a time period r he 1 h an as 1 g a 1 g of minutes. dunhg h? metal h h which For testing purposes, the clear varnish or the enamel, pose the coating composltlons of this lnventlon are prefrespectively is applied to deepdrawn Steel sheets of a "2 h d th t l t f h thickness of 1 mm. and glass panes at room temperature h h cure W1 ca a ys s o t 1 present mveh and then baked. The thickness of the film coatings being tlon exhlblt the same satisfactory properties as the coat- 30 tested is in all examples 3040' mgs cured f l Prevloushf customhry catalyst The hardness test is performed according to German toll enesulfonlc acid and surprisingly exhibit an excellent Industrial Standard DIN 53 157 The elasticity is maas l;, i: :g th am t t t f ured according to DIN 53,156. The impact deformability C 3: he ys empera is determined by the impact depression device 226/D proyc e 6 Op h h (Erichsen, Hemer-Sundwig). In this device, a hemisphere The hialelc acld hh oxahc acld can he admlxed whh having a radius of 10 mm is suddenly impressed into the the coatmg. homposlhoh shorhy Pnor to h haklhg metal sheet from the back of the varnish side by means .However 1t 15 prefhrred to h' the dlcarhoxyhc i of a falling weight. By varying the falling height of the zgig g i gg gg the ester mlxture and thereafter hhx 40 weight, the depression can be varied. The depression value p (in mm.) is indicated at which the varnish layer begins Without further elaboration, 1t 1s belleved that one to teal. The adhesion is tested by measuring the deep ih m the art hslhg h precedlhg descnphoh drawability of the varnish over the center of a 90 cross uhhze the Present lmjenhoh to fullest extent The cut. The depression value is indicated (in mm at which lowmg preferred Specific emhodlmehts fi h h to he 5 the coating is detached from the test metal sheet. construed as merely lllustratlve, and not llmltatlve of the The two figures appearing in the column Solvent remainder of the dlscloshre m any way whatsoever sistance characterize the swelling and scratch sensitivity EXAMPLES of the baked varnish film after 15 minutes of constant exposure to xylene at room temperature. The first number Produchon of the Ester is the swelling in three evaluation stages (1=unswelled; A mixture of 65.1 g. of ethylene glycol (1.05 mol), 2=slightly swelled; and 3 =greatly swelled) and the 79.8 g. of 1,2-propaned1ol (1.05 mol), 74g. of phthalic second number is the scratch sensitivity, likewise in three anhydride (0.5 mol), and 73 g. of adlplc acld (0.5 mol) is evaluation stages (1=scratchproof; 2=minor scratch rchcated under agitation and whlle passing a gentle nitrogen sistance; and 3=no scratch resistance).

Hard- Deep l o Impact acc.

l n number Amount and type of catalyst plastz'liO, (Hm???) (see.) (111111.) (11 1 1?) (mhh) if; oi h h h hg 1 0.5% by wt. p-toluene-sullonic acid :30:50 /30 168 7.3 4 2.3 1/1 White.

/30 166 7.2 5 3.7 1/1 Do. /30 98 6. 2 2 3. 1 1/1 Do. 180/30 70 4.0 1 1.9 1/1 Yellow. 200/30 84 1.5 1 1.1 1/1 Yellowbrown. 220/30 97 0.9 1 0.8 1/1 Brown. 2..:;..-.-;:.-:.- 1% bywt.monobuty1phosphate 70=30=50 150/30 11 10.8 5 10.0 2/3 whim;

165/30 16 9.7 5 9.9 2/3 Do.- 180/30 58 8.7 1/2 Do. 200/a0 133 7.6 1 1 Do. 220/30 6.4 1/1 Do. 3...:;:;.::.'. 1% by Wt. H3PO45535;332:332; 70:30z0 150/30 53 9.4 9.5 1/1 Clear.

165/30 80 9.3 5 9.3 1/1 Do.- /30 104 9.0 5 9.0 1/1 Do. 200/30 101 7.3 3 6.4 1/1 Do; 220/30 149 6.4 1 5.9 1/1 Yellowish:

THE-Continued Hard- Deep ness, drawaace. to bility Impact Weight ratio, Baking DIN DIN depres- Adhe- Solvent Example esterzaminoconditions 53157 53156 sion sion reslst- Appearance number Amount and type of catalyst plastTiO C./min.) (see) (mm.) (mm.) (mm.) anee of coating 4 1% by wt. phthallc anhydrlde 70:30:0 150/30 Films are tacky 165/30 Films are tacky 180/30 16 10 2/3 Clear. 200/30 17 2/3 D0. 220/30 10 2/3 Yellowish.

5 1% by wt. maleic acid...; 70:30:50 150/30 156 8. 4 5 6. 2 1/1 White 165/30 160 8. 4 5 7. 8 1/1 D0. 180/30 162 8. 2 5 6. 6 1/1 Do. 200/ 156 8. 1 5 6. 4 1/1 D0. 220/30 159 7. 8 5 6. 6 1/1 Do.

6 1% by wt. maleic acld....;.;.*..; 70:30z0 150/30 173 9.4 5 9. 4 1/1 Clear.

165/30 170 9. 6 5 9. 5 1/1 Do. 180/30 176 9. 4 5 9. 4 1/1 Do. 200/30 166 9. 8 5 9. 3 1/1 D0. 0/30 165 9. 9 5 9. 4 1/1 D0.

7... 1% by wt. oxalic acid.....';:..;.;:.- 70:30:50 150/30 92 8.8 5 8.3 1/2 White.

165/30 121 8. 5 5 8. 0 1/1 D0. 180/30 157 7. 9 5 6. 1 l/l Do. 200/30 173 7. 5 5 7. 4 1/1 D0. 220/30 173 6. 3 5 6. 0 1/1 Slightly yellow.

8 1% by Wt. phthalle acid...-.;-..-:.:.;...; 70:30:50 150/30 28 9. 5 5 9. 4 2/2 White.

165/30 34 9. 5 5 9. 9 2/2 Do. 180/30 56 9. 4 5 9. 5 2/ 2 Do. 200/30 84 8. 9 5 8. 1 2/1 Do. 220/30 149 7. 6 5 7. 2 1/1 Do.

9 1 o by W17. adi i0 801d-.;.;-;.';.;-;.;:.'-; 70:30:50 150/30 Tacky films 7 p 165/30 Tacky films 180/30 12 9. 6 5 9. 5 2/3 White. 200/30 59 8. 5 5 7. 6 2/2 D0. 220/30 96 6. 7 4 6. 4 2/1 D0.

10 1% by wt. malele auhydrlde 70:30:0 150/30 19 10 5 10 2/2 Clear.

165/30 19 10 5 10 2/2 DO. 180/30 21 10 5 10 2/2 Do. 200/30 30 10 5 10 2/2 Yellow. 220/30 41 10 5 9. 5 2/2 D0.

The preceding examples can be repeated with similar success by substituting the generically or specifically dedescribed reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

What is claimed is:

1. In a heat curing coating composition containing, as the binder (A) 45-15% by weight of an aminoplast or a lowmolecular precursor thereof; and

(B) 55-85% by weight of at least difunctional esters containing predominantly hydroxyl groups and optionally carboxyl groups as the functional groups and having an average molecular weight of less than 600 and produced by the esterification of I. an alcohol reactant consisting essentially of:

(1) 0-50 molar percent of one or more aliphatic polyols of 3 or 4 hydroxyl groups and 3-6 carbon atoms, and (2) 100-50 molar percent of a diol component consisting essentially of: (a) at least '70 molar percent of one or both of ethylene glycol and 1,2-propanediol, and (b) up to 30 molar percent of one or more other aliphatic or cycloaliphatic diols whose hydroxyl groups are separated by 2-8 carbon atoms, and 0 to 2 of the carbon atoms in the chain are substituted by oxygen atoms which are separated from each other and from the hydroxyl groups by at least 2 carbon atoms, and II. an acid mixture consisting essentially of:

(1) 80-20 molar percent of one or more aro matic or cycloaliphatic dicarboxylic acids whose carboxyl groups are positioned ortho or meta or a functional acid derivative thereof convertible to an ester of the alcohol reactant, and

(2) 20-80 molar percent of at least one saturated aliphatic dicarboxylic acid of 4-12 carbon atoms or a functional acid derivative thereof convertible to an ester of the alcohol reactant,

the improvement wherein the coating composition contains as a curing catalyst about 0.7-2.0% by weight of one or both of maleic acid and oxalic acid.

2. A coating composition according to Claim 1 containing about 1.01.5% by weight of the catalyst.

3. A coating composition according to Claim 1 containing maleic acid as the catalyst.

4. A coating composition according to Claim 3 containing about 1.0-1.5 by weight of the catalyst.

5. In a process for curing a coating composition containing, as the binder (A) 45-15% by weight of an aminoplast or a lowmolecular precursor thereof; and (B) 55-85% by weight of at least difunctional esters containing predominantly hydroxyl groups and optionally carboxyl groups as the functional groups and having an average molecular weight of less than 600 and produced by the esteriiication of (I. an alcohol reactant consisting essentially of:

(1) 0-50 molar percent of one or more aliphatic polyols of 3 or 4 hydroxyl groups and 3-6 carbon atoms, and h (2) -50 molar percent of a diol component consisting essentially of: (a) at least 70 molar percent of one or both of ethylene glycol and 1,2-propanediol, and (b) up to 30 molar percent of one or more other aliphatic or cycloaliphatic diols whose hydroxyl groups are separated by 2-8 carbon atoms, and 0 to 2 of the carbon atoms in the chain are substituted by oxygen atoms which are separated from each other and from the hydroxyl groups by at least 2 carbon atoms, and

II. an acid mixture consisting essentially of:

(1) 80-20 molar percent of one or more aromatic or cycloaliphatic dicarboxylic acids whose carboxyl groups are positioned ortho or meta or a functional acid derivative thereof convertible to an ester of the alcohol reactant, and

(2) 20-80 molar percent of at least one saturated aliphatic dicarboxylic acid of 4-12 carbon atoms or a functional acid derivative thereof convertible to an ester of the alcohol reactant,

the improvement which comprises employing as curing catalyst about 07-20% by weight of one or both of maleic acid and oxalic acid.

6. A process according to Claim 5 which comprises employing about 1.0-1.5 by weight of the catalyst.

7. A process according to Claim 6 wherein the catalyst is maleic acid.

8. A process according to Claim 7 which comprises employing about 1.01.5% by weight of the catalyst.

5 References Cited UNITED STATES PATENTS 3,678,128 7/1972 Riemhofer et a1. 260-850 3,691,258 9/1972 'Riemhofer ct al 260-850 10 2,600,100 6/1952 'Evans et a1. 260-850 3,152,095 10/1964 Tropp et a1. 260-850 2,918,452 12/1959 Kun et al. 260-850 2,871,209 1/1959 Shelley 260-850 15 2,683,100 7/1954 Edgar et a1. 260-850 JOHN C. BLEUTGE, Primary 'Examiner US Cl. X.R.

117-124 E, 132 BF, 161 K, 161 LN; 260-39 R, 40 R, 

